Modeling Spatial Patterns of Dissolved Oxygen and the Impact Mechanisms in a Cascade River

Ming Zhong,Kun Li,Guoping Tang,Huabo Jiang,Shanxia Liu,Tao Jiang

doi:10.3389/fenvs.2021.781646

Ming Zhong, Kun Li + Show 4 more

Open Access

https://doi.org/10.3389/fenvs.2021.781646

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Abstract

Dissolved oxygen (DO) concentration is an essential indicator for assessment of river ecosystems. A hydrodynamic and water quality mathematical model coupling one-dimensional and two-dimensional models is developed in this study. The characteristics of study area, flow velocity, temperature, and organic contamination are taken as consideration in the scenario setting. The changing processes of DO concentration are simulated in different scenarios, and the effects on DO concentration are discussed. Results indicate that: 1) A negative relation was present between DO concentration in Yongjiang River and releasing discharge of the Laokou hydro-project, since reoxygenation is greater than oxygen consumption along the river, DO concentration increases from upstream to downstream. 2) DO concentration increases with the releasing of DO in the water, which also varies along with the releasing of biochemical oxygen demand (BOD) concentration. Laokou exhibits the greatest increase of BOD, which ranges from 0.1 mg/L to 0.75 mg/L 3) The increasing of water temperature results in increased reoxygenation and a decrease in oxygen consumption. Our study shows that the water temperature increased from 19°C to 29 °C, and correspondingly saturated DO decreased from 9.25 mg/L to 7.54 mg/L. The study provides scientific support for ecology operation in the cascade river, and is expected to improve the water environment by reservoir regulation.

Highlights

The dissolved oxygen (DO) concentration in a river is an essential indicator of the ecosystem assessment
The results indicate that DO concentration was negatively correlated with water temperatures
In sewage inlets into the river reach, since the BOD concentration is low in the upstream water and in polluted water, reoxygenation is greater than oxygen consumption in the study region, which causes DO concentration to increase and water quality to improve

Summary

Introduction

The dissolved oxygen (DO) concentration in a river is an essential indicator of the ecosystem assessment. DO decreases in rivers impacts the biological activities and results in reductions in benthic animal populations (Bu et al, 2021). A low DO concentration may slow the degradation of pollutions, weaken the capacity of water’s self-purification, and even decrease the quality of the aquatic ecosystem. According to the resources and consuming paths, DO balance is affected by atmosphere oxygen production, photosynthesis, and biochemical consumption (e.g., degradation of organic matter, degradation of sediment pollutants, respiration of animals and plants). The DO budget in a river is related to the spatial-temporal change of temperature, Spatial Patterns of Dissolved Oxygen salinity, nutrients, underwater topography, and wind (Hutchins et al, 2021). In the one-way river, DO concentration is mainly affected by upstream runoff, while in the tidal river, the mechanism of DO concentration can be more complex due to the tidal effect (Li et al, 2020)

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